Leopold RužičkaForMemRS (Croatian pronunciation: [rǔʒitʃka];[3] 13 September 1887 – 26 September 1976)[5] was a Croatian-Swiss scientist and joint winner of the 1939 Nobel Prize in Chemistry[6] who worked most of his life in Switzerland. He received eight honoris causa doctorates in science, medicine, and law; seven prizes and medals; and twenty-four honorary memberships in chemical, biochemical, and other scientific societies.

Ružička attended the classics-program secondary school in Osijek. He changed his original idea of becoming a priest and switched to studying technical disciplines. Chemistry was his choice, probably because he hoped to get a position at the newly opened sugar refinery built in Osijek.

Ružička's first works originated during that period in the field of chemistry of natural compounds. He remained in this field of research all his life. He investigated the ingredients of the Dalmatianinsect powder Pyrethrum (from the herb Tanacetum cinerariifolium), a highly esteemed insecticide found in pyrethrins. In this way, he came into contact with the chemistry of terpene, a fragrant oil of vegetable origin, interesting to the perfumeindustry. He intended to start individual research and even started successful and productive cooperation with the Chuit & Naef Company (later known as Firmenich) in Geneva.

In 1916–1917, he received the support of the oldest perfume manufacturer in the worldHaarman & Reimer, of Holzminden in Germany. With expertise in the terpene field, he became senior lecturer in 1918, and in 1923, honorary professor at the ETH (Eidgenössische Technische Hochschule) as well the University in Zurich. Here, with a group of his doctoral students, he proved the structure of the compounds muscone and civetone, macrocyclic ketone scents derived from the musk deer (Moschus moschiferus) and the civet cat (Viverra civetta).[7] These were the first natural products shown to have rings with more than six atoms, and at the time that Ružička inferred that civetone as having a 17-member ring,[8] synthetic techniques were only known for rings of up to eight members.[9] Muscone had been isolated in 1904[10] but was not identified as 3-methylcyclopentadecanone[11] until Ružička suspected a macrocycle, having characterised civetone. He also developed a method for synthesising macrocycles, now known as the Ruzicka large ring synthesis,[12] which he demonstrated by preparing civetone in 1927.[9][13]

In 1921, the Geneva perfume manufacturers Chuit & Naef asked him to collaborate. Working here, Ružička achieved financial independence, but not as big as he had planned, so he left Zurich to start working for the Ciba, a Basel-based company. In 1927, he took over the organic chemistry chair at Utrecht University in Netherlands. In Netherlands he remained for three years, and then returned to Switzerland, which was superior in its chemical industry.

Back to Zurich, at ETH he became professor of organic chemistry and started the most brilliant period of his professional career. He widened the area of his research, adding to it the chemistry of higher terpenes and steroids. After the successful synthesis of sex hormones (androsterone and testosterone), his laboratory became the world center of organic chemistry.

In 1939 he won the Nobel prize for chemistry with Adolf Butenandt.[6] In 1940, following the award, he was invited by the Croatian Chemical Association, where he delivered a lecture to an over packed hall of dignitaries. The topic of the lecture was From the Dalmatian Insect Powder to Sex Hormones. In 1940 he became a foreign member of the Royal Netherlands Academy of Arts and Sciences.[4] During the World War II, some of his excellent collaborators were lost, but Ružička restructured his laboratory with new, younger and promising people; among them was young scientist and future Nobel Laureate Vladimir Prelog. With new people and ideas new research areas were opened.

Following 1950, Ružička returned to chemistry, which had entered a new era of research. Now he turned to the field of biochemistry, the problems of evolution and genesis of life, particularly to the biogenesis of terpenes. He published his hypothesis, the Biogenetic Isoprene Rule (that the carbon skeleton of terpenes is composed variously of regularly or irregularly linked isoprene units), which was the peak of his scientific career.[14] Ružička retired in 1957, turning over the running of the laboratory to Prelog.